The present invention relates broadly to magnetic bubble domains, and in particular to an associative bubble memory apparatus.
In the present state of the art computer memories, information is stored in one of two magnetic states on a magnetic material. The unique characteristics of magnetic materials enable them (1) to hold one of two magnetic states (direction of magnetization) in the absence of power (nonvolatility), (2) to be quickly alterable between states with a small amount of input power, (3) to be readable at high speeds by means resulting in a system-compatible electric current flow, and (4) to store large amounts of information by providing extremely high geometric densities of magnetization. These characteristics have caused magnetic memory devices to supersede most prior attempts at memory design, and such devices will continue to be useful for a long time into the future. Electrostatic storage in cathode ray tubes and mercury delay lines has been made obsolete by magnetic cores and drums.
Magnetic core memories may be classified as discrete stationary medium memories. Each core is capable of storing only one bit. A "zero" is represented by magnetizing the doughnut-shaped core so that the flux direction is, say, clockwise, while a "one" is represented by the opposite direction of magnetization. The core is set by a current flowing in a wire through the center of the core. A rectangular grid of wires, with a core surrounding each wire crossing, is called a plane. Selective setting of cores is accomplished by passing half currents (half the amount required for switching) through the grid wires. Only those cores will be set where the half currents coincide and thus exceed the switching threshold of the cores. A stack of planes is a memory array. For a word length of 16 bits, an array of 16 planes, each holding 1024 cores, would be called a 1024 word, coincident current, word addressable memory.
The speed of core memories is limited by the switching time of the cores, the length of the wires in the arrays, and the pulse length and frequency of the drive and recovery time of the read or sense amplifiers.